Plural articles of like kind are frequently gathered in unitary packages for ease in handling during shipment and storage. For instance, wood and paper products, steel, bricks, concrete blocks, concrete slabs, pipes, poles, plywood sheets, particle board, and the like, are frequently packaged to facilitate handling of the articles.
Lumber products are typically manufactured in a variety of lengths, ranging from eight feet up to twenty feet, e.g., conventional dimension lumber is manufactured in lengths of 8, 10, 12, 14, 16, 18 and 20 feet, respectively. Following manufacture, this lumber is sorted according to length, width, thickness and grade and then bundled in packages according to the dimensions and grade of the lumber. That is, all boards having nominal dimensions of two inches by eight inches by eight feet, for example, and having a pre-determined grade, i.e., grade 1, grade 2 etc., are bundled together in a package consisting of from about 200 to 300 boards, and these packages are then shipped to various points of use and/or sale. Similar packages are formed of lumber having different dimensions and grade.
Various machinery has been developed in the prior art to automatically sort and stack lumber products. Some prior art machinery is capable of handling lumber in a variety of lengths and some includes independently operable stacker arms. However, all such prior art machinery is relatively complex and expensive in construction and operation. Moreover, conventional lumber stacking machinery sometimes will not operate quickly enough to keep up with other pieces of equipment in a lumber mill. Additionally, conventional machinery generally does not have any means to enable the stacker to keep operating while maintenance or repair is being performed, whereby failure or breakdown in one part of the machine will generally necessitate shut down of the entire machine.
Accordingly, there is need for lumber stacking machinery that is simple and inexpensive in construction and operation, and which operates at a relatively high speed so that stacking of the lumber to form packages can proceed at a pace equivalent to the pace of operation of other machinery in the process. Further, such machinery should be capable of continued operation while maintenance or repair is being performed, and should be capable of handling all normal sizes of lumber products without requiring adjustment or modification of the machine.